1. Field of the Invention
The present invention relates to a driver circuit for power device. More particularly, it relates to a driver circuit for power device preventing malfunction or breakdown while allowing scaledown and cost reduction thereof.
2. Description of the Background Art
FIG. 8 is a circuit diagram illustrating a three-phase inverter circuit and a driver circuit thereof in the background art. A three-phase inverter circuit 100 in FIG. 8 includes high side switching elements 101, 103 and 105, and low side switching elements 102, 104 and 106. The three-phase inverter circuit 100 further includes diodes 107, 109 and 111 respectively connected in parallel to the high side switching elements 101, 103 and 105, and diodes 108, 110 and 112 respectively connected in parallel to the low side switching elements 102, 104 and 106.
The high side switching elements 101, 103 and 105, and the low side switching elements 102, 104 and 106 each receive power supplied thereto from a power source 113. Interconnect lines for connecting the high side switching elements 101, 103, 105 and the low side switching elements 102, 104, 106 have respective self-inductances as indicated by reference numerals 114 through 121 in FIG. 8. The high side switching elements 101, 103 and 105, and the low side switching elements 102, 104 and 106 are each an IGBT (insulated gate bipolar transistor).
A Load such as a three-phase motor 122 is connected to the three-phase inverter circuit 100. A high side switching driver circuit is connected to each one of the high side switching elements 101, 103 and 105, and a low side switching driver circuit is connected to each one of the low side switching elements 102, 104 and 106. In FIG. 8, only a high side switching driver circuit 200 connected to the high side switching element 101, and a low side switching driver circuit 300 connected to the low side switching element 102 are shown. Those driver circuits respectively connected to the high side switching elements 103 and 105, and to the low side switching elements 104 and 106 are omitted. The inverter circuit, the high side switching driver circuit, and low side switching driver circuit constitute a driver circuit for power device.
The high side switching driver circuit 200 connected to the high side switching element 101 includes an emitter follower circuit, a high voltage IC 201, and a power source 202 and capacitors 203 and 204 for driving these circuits. An NPN transistor (on-side emitter follower transistor) 205 and a PNP transistor (off-side emitter follower transistor) 206 constitute the emitter follower circuit of the high side switching driver circuit 200. Emitter terminals of the transistors 205 and 206 are respectively connected to resistors 207 and 208, and then commonly connected to the gate terminal of the high side switching element 101. The capacitor 203 is provided between a high-voltage side power source terminal Vb and a high-voltage side reference terminal Vs in the high voltage IC 201, and the capacitor 204 is provided between a low-voltage side power source terminal Vcc and a low-voltage side reference terminal Vss in the high voltage IC 201. An input terminal IN of the high voltage IC 201 receives a driving signal Hi-IN of the high side switching element inputted thereto. The driving signal Hi-IN is outputted from an output terminal OUT of the high voltage IC 201 to the emitter follower circuit.
Similarly, the low side switching driver circuit 300 connected to the low side switching element 102 includes an emitter follower circuit, a high voltage IC 301, and a power source 302 and capacitors 303, 304 for driving these circuits. An NPN transistor 305 and a PNP transistor 306 constitute the emitter follower circuit of the low side switching driver circuit 300. Emitter terminals of the transistors 305 and 306 are respectively connected to resistors 307 and 308, and then commonly connected to the gate terminal of the low side switching element 102. The capacitor 303 is provided between a high-voltage side power source terminal Vb and a high-voltage side reference terminal Vs in the high voltage IC 301, and the capacitor 304 is provided between a low-voltage side power source terminal Vcc and a low-voltage side reference terminal Vss in the high voltage IC 301. The capacitors 204 and 304 are connected to a power source 309. AN input terminal IN of the high voltage IC 301 receives a driving signal Low-IN of the low side switching element inputted thereto. The driving signal Low-IN is outputted from an output terminal OUT of the high voltage IC 301 to the emitter follower circuit.
As shown in FIG. 8, clamping diodes 209 and 310 are further provided to the high voltage ICs 201 and 301, respectively. The clamping diodes 209 and 310 each have an anode connected to the low-voltage side reference terminal Vss, and a cathode connected to the high-voltage side reference terminal Vs. As disclosed in Japanese Patent Application Laid-Open No. 10-42575 (1998), the clamping diodes 209 and 310 are operative to protect the high voltage ICs 201 and 301 from negative potential surge (hereinafter referred to as negative surge). Such negative surge is generated by the variation in current with respect to time (di/dt) and the self-inductances 114 through 121 of the interconnect lines when the high side switching elements 101, 103 and 105, or the low side switching elements 102, 104 and 106 are switched for driving the load.
However, the clamping diodes 209 and 310 may not be operative enough to sufficiently protect the high voltage IC 201 of the high side switching driver circuit and the high voltage IC 301 of the low side switching driver circuit, respectively. As a countermeasure therefor, in the three-phase inverter circuit and the driver circuit thereof shown in FIG. 8, a resistor 400 is interposed between the emitter terminal of the low side switching element 104 and the power source 309. When the negative surge is generated, negative surge current flowing in the clamping diodes 209 and 310 is limited so that the high voltage ICs 201 and 301 can be protected. Such technique is disclosed in PCT Publication No. WO 01/59918.
When only the high side switching element 101 and the low side switching element 104 are in ON state and the high side switching element 101 is switched to OFF state, the negative surge is generated in the three-phase inverter circuit and the driver circuit thereof in FIG. 8, the detail of which will be given below.
When only the high side switching element 101 and the low side switching element 104 are in ON state, current supplied from the positive pole of the power source 113 flows through the high side switching element 101, self-inductance 114, load 122, self-inductance 117, low side switching element 104, and the self-inductance 121 in this order. The current then returns to the negative pole of the power source 113.
Next, when the high side switching element 101 is switched to OFF state, the current flowing through the load 122 follows the different path. Namely, the current flows through the load 122, self-inductance 117, low side switching element 104, self inductance 120, diode 108, self-inductance 115, and the load 122 in this order. In the course of this current flow, the self inductances 114, 115, 120 and 121 of the interconnect lines generate the negative surge.
When such negative surge is generated, the low-voltage side reference terminal Vss and the high-voltage side reference terminal Vs in the high voltage IC 201 of the high side switching driver circuit 200 receive voltage applied thereto. This voltage is the sum of induced voltages of the self-inductances 114, 115 and 120, and forward voltage of the diode 108. The clamping diode 209 is then switched to ON state, whereby forward voltage of the clamping diode 209 is applied between the low-voltage side reference terminal Vss and the high-voltage side reference terminal Vs in the high voltage IC 201 that are connected in parallel to the clamping diode 209.
As seen from FIG. 8, further, the resistor 400 is provided in the path between the low-voltage side reference terminal Vss and the high-voltage side reference terminal Vs in the high voltage IC 201. The current flowing through the clamping diode 209 is thereby limited. Therefore, the negative surge current can be limited by the resistor 400, whereby the forward voltage of the clamping diode 209 can be limited to a level that causes no malfunction or breakdown of the high voltage IC 201. As the resistor 400 is increased in resistance value, voltage drop in the resistor 400 becomes greater. The forward voltage of the clamping diode 209 can be limited accordingly.
According to the three-phase inverter circuit and the driver circuit thereof shown in FIG. 8, the high voltage IC 201 of the high side switching driver circuit and the high voltage IC 301 of the low side switching driver circuit can be protected from the negative surge generated by the self-inductances 114 through 121 of the interconnect lines. However, in the low side switching driver circuit for the low side switching elements 102, 104 and 106 shown in FIG. 8, the power sources 302 and 309 should be provided to each one of the elements 102, 104 and 106, resulting in increase in cost for the power source. For scaledown and cost reduction of the low side switching driver circuit for each of the low side switching elements 102, 104 and 106, the power sources 302 and 309 should be combined and the high voltage IC 301 should be eliminated.
It is therefore an object of the present invention to provide a driver circuit for power device including a high side switching driver circuit and a low side switching driver circuit. More particularly, it is the object of the present invention to protect a high voltage IC of the high side switching driver circuit from negative surge generated by a self inductance of an interconnect line while requiring no high voltage IC in the low side switching driver circuit, to realize scaledown and cost reduction of the driver circuit.
According to the present invention, the driver circuit for power device includes a plurality of low side switching elements for constituting an inverter circuit, a plurality of high side switching elements for constituting the inverter circuit, a plurality of high side switching driver circuits, and a plurality of low side switching driver circuits. The plurality of low side switching elements each have one terminal connected to a load, and other terminal connected to a low potential line of the inverter circuit. The plurality of high side switching elements each have one terminal connected to the load, and other terminal connected to a high potential line of the inverter circuit. The plurality of high side switching driver circuits respectively drive the plurality of high side switching elements. The plurality of high side switching driver circuits each include a high voltage IC. The plurality of low side switching driver circuits respectively drive the plurality of low side switching elements. The plurality of low side switching driver circuits each include a first low potential power source line, a second low potential power source line, a first high potential power source line, and a second high potential power source line each connected to the high voltage IC. The plurality of low side switching driver circuits each include a first power source, a first capacitor, a second capacitor, a first current limiting element, and second current limiting elements. The plurality of low side switching driver circuits are commonly connected to the first power source. The first capacitor is connected to the first power source through the first low potential power source line and the first high potential power source line. The second capacitor is connected to the first power source through the second low potential power source line and the second high potential power source line. The first current limiting element is provided between a node between the first low potential power source line and the first capacitor, and the second low potential power source line. The second current limiting elements are respectively provided on the second low potential power source line and the second high potential power source line for connecting the first power source and the second capacitor.
The driver circuit for power device includes the first current limiting element provided between the first power source to which the plurality of low side switching driver circuits are connected, and the low side switching element. Further provided are the second current limiting elements on the interconnect lines for connecting each of the plurality of low side switching driver circuits and the high voltage IC. Therefore, the high voltage IC of the high side switching driver circuit can be protected from negative surge. Further, as the driver circuit for power device requires no high voltage IC in the low side switching driver circuit, scaledown and cost reduction are realized.